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Reissued Feb..23, 1932 UNITED STATES PATENT OFFICE MORGAN K. ARMSTRONG,OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR, BY MESNE ASSIGNMENTS, TOUNITED STATES GYPSUM COMPANY Monomer COMPOSITION No Drawing. Originalapplication filed April 29, 1920, Serial No. 377,421. Renewed JMarch 4,1927. OriginalNo. 1,641,611, dated September 6, 1927; Application forreissue filed October 26, 1929. Serial This invention relates to animproved plastic mixture and relates more particularly to a moldingcomposition suitable for the cores of plaster boards or for use inmaking molded forms and the like.

The object of the invention is to produce a novel and useful plasticmixture, more particularly adapted for use as a body, core or filler forplaster Wall boards, for molded forms and the like.

The plastic mixture is of the kind described in Letters Patent No.1,331,554 granted to m e February 2 1, 1920, and includes as its mainingredient a full clay, or soil containing a comparatively largeproportion of clay.

T e clay or soil is deflocculated as in my earlier patent, first mixingit with Water in a suitable receptacle and then subjecting it to theaction of an electrolyte, as sodium phosphate. The electrolyte is addedin an amount suflicient to precipitate the greater part of the solubleconstituents of the clay, the amount varying with different clays andbeing determined by experiment.

After or during the process of deflocculation, a very small percentage(one-half to three-fourths of one percent) of some organic colloid suchas starch or dextrine, is added and thoroughly dissolved in the mixture.

To the processed clay, I then add, in a liquid state and either cold orhot, bitumen,

asphalt, coal tar or other water-proofing material. The amount ofwater-proofing material addedto the processed clay should preferablyapproximate the volume of Water added to the clay in the process ofdeflocculation. The water-proofing material is thoroughly incorporatedby agitation with the treated clay to form an emulsion.

The emulsion thus made may be produced in large quantities and may beplaced in suitable receptacles to be kept on hand, ready for use whenneeded, to make the improved plastic mix.

When desired for use in a plastic mix for making plaster board, moldedproducts, or

the like, finely ground calcined gypsum is added to the clay mix orslurry contamlng the bituminous substance, and the two are thoroughlymixed together. The plastic mix is then ready for immediate use, as forexmix is to be used. I In the case of the use of the plastic mix inmaking plaster board, the proportions of the clay mix and of thecalcined gypsum are 40% of gypsum and 60% of the clay mix emulsion.

The combined Water of the hydrates of the clay mix, as Well as the wateradded in the process of deflocculation, provide the water for hydratingthe gypsum when the plastic mix is being used for any of its intendedpurposes.

The bitumen, asphalt, coal tar or like Wat-- ter-proofing content of theplastic mix not only acts to make it Waterproof, but in addition it addsgreatly to the tensile and compressive strength of the mixture when dry.Thus when the mixture is used for making board for example, theincreased strength of the mixture greatly increases the resistance ofthe board to bending, shearing or other breaking strains.

Again, the particles of plaster possess greatly increased adherence, sothata nail driven through the plaster, as when nailing a board made ofthe plaster to studding, Will not break the plaster. The new plaster isthus an efficient nailing mixture. The excess of clay, over and abovethat necessary for emulsification of the asphalt, acts as a fillingagent in the final composition, and this filling agent is firmly heldtogether by the binding agent which is composed of bothethe asphalt andthe gypsum or. other cementitious mater al. aphalt by combining with theWater and setting up as a binding agent for the filling agent and thecomposition as a whole.

I would state in conclusion that While the above disclosure represents apractical embodiment of my inventionfI do not wish to .limit myselfprecisely to these details, since The gypsum serves to de-emulsify thevaried, without departing from the spirit of the invention as defined inthe appended claims.

Having thus described my invention, I 5 claim as neW,-and. desire tosecure by Letters Patent 1. A rigid, waterproof, nail penetrableWallboard comprising a plastic mix of defiocculated clay, a bituminousmaterial, and

calcined gypsum in such proportions that the product has the propertiesspecified.

2. A rigid, nail penetrablewallboard comprising a plastic mixture of alarge percentage of calcined gypsum, Water and bitumen,

said bitumen having been emulsified to render it miscible with water byan emulsifying agent such as defiocculated clay.

3. A rigid, nail penetrable wallboard comprising a plastic mixture ofabout 40% calcined gypsum, and about 60% of a mixture containingasphalt, water and a filling agent.

MORGAN K. ARMSTRONG.

